This invention relates to the production of low-carbon steel sheet for electrical applications and, more particularly to an improved method for producing fully-processed, low-carbon, non-silicon bearing steel sheet having magnetic properties which are especially suited to its use in the magnetic cores of electrical equipment.
The development of silicon containing steels around the first part of this century has made possible the production of efficient and more powerful electrical equipment, a factor which played an important role in the rapid growth of the electrical-power industry. Such steels are characterized by excellent magnetic properties, i.e., high magnetic permeability, high electrical resistance and low hysteresis losses, but they are relatively expensive because of the exacting parameters required in their production.
This high cost factor may be acceptable where exceptional magnetic properties are required, such as, for example, in the case of large transformers or highest efficiency motors or generators and the like, but there are many instances where superior magnetic properties are not required for efficient operation of electrical equipment, such as, for example, in the case of consumer appliances and similar small electrical equipment. In those instances the high cost of the silicon-containing steel could not be justified.
As more and more such small electrical equipment was developed for the marketplace, the demand for a less costly steel became greater and this demand was met by the production of non-silicon bearing electrical steels. Such steels are commonly produced either from a low-carbon steel heat or by a decarburization procedure wherein plain carbon steel strip is subjected to annealing, e.g., open coil annealing, followed by a critical straining to obtain elongation within certain limits. The steel is usually sold in semi-processed condition so that it must subsequently be annealed by the customer, usually after stamping or similar article production procedures. The electrical steel produced by such methods was clearly less expensive than the silicon-containing steel, but it was still more expensive than desired for many applications and thus there has been a continuing need for electrical steel which would not only have the desired magnetic properties required of smaller electrical equipment but also would be fully-processed and satisfy the cost-factor requirements of present day economics.
This continuing need for such a low-cost steel has now been met in the present invention which will be more fully described below.